Spatial Uncertainty in Depth Averaged Velocity Determined from Stationary, Transect, and Longitudinal ADCP Measurements

Abstract

This study builds upon established methods for using acoustic Doppler current profilers (ADCPs) to measure velocities to include another measurement technique—longitudinal measurements—which are increasingly being used in open channel flow studies. Longitudinal measurements are collected in paths that parallel the streamwise direction as opposed to transect measurements, which are collected perpendicular to the flow direction. This study analyzed ADCP data that were collected concurrently using stationary, transect, and longitudinal collection methods in order to determine which method can be used to most effectively develop interpolated velocity maps. Data from the Pecatonica River in Freeport, Illinois, and the St. Joseph River in Berrien Springs, Michigan, were used as case studies for comparing measurement techniques. To compare interpolated velocities calculated using the longitudinal data collection technique with a traditional transect data collection scheme, the variables of data density and data collection effort were systematically altered to investigate both methods. Data collection effort time was utilized to provide equivalent velocity comparison between the ADCP data collection techniques. Plots that compared interpolated transect and longitudinal velocities to transect and stationary data illustrated that the longitudinal interpolated velocities match the known data and mimic the cross section velocity trend better than the interpolated transect depth averaged velocities. The longitudinal measurement technique was substantially better at describing the depth averaged velocity variation for the river reaches investigated.